From my professional medical view, there are only two answers to this:
1) if you are very serious about hygiene there is absolutely no other option than discarding the cannula after a single use. It is entirely impossible to clean long tubing in a safe way with any method any of you has access to, so forget about it.
2) if you are relaxed about all this, you can re-use and switch cannula at random. The risk of serious infection is very low unless you have some form of inmunodeficiency and the person you have taken the used cannula from has a currently active infection. Even then, the most likely infections are things like common cold…not exactly threatening.
This discussion is intellectually interesting, but in order to exit the rabbit hole of research of which disinfection method would be better/safer, I just bought a set of 100 cannulas for below 40,- EUR (including shipping), and I think I will just throw them away regularly.
Even better is sell a fresh cannula to the passenger for €30
Or give them the option for a used one and see which one they prefer!
Peter wrote:
Yes it is used in swimming pools too, but a lot of bugs can and do exist in swimming pools despite its use.
I am not sure that is really relevant, as the aim in a pool is to maintain the level at between 1 and 3 ppm, and often, the level will be found to be lower.
Alcohol at less that 50% is very ineffective as well.
As I said earlier, I think there is a reasonable amount of research to suggest alcohol is less effective, but I dont suppose it matters, any reasonable disinfection will probably suffice, or, as you say, just provide a new one.
Yes it is used in swimming pools too, but a lot of bugs can and do exist in swimming pools despite its use.
Hence I think alcohol, and carefully blowing it out, is better for cannula cleaning.
Even better is sell a fresh cannula to the passenger for €30 
Sodium hypochlorite is actually well tolerated by the body in low concentrations and can and is used in drinking water as a means of controlling purity.
There some reading here about certain drawbacks of alcohol especially regarding anything associated with the airways.
https://www.cdc.gov/infectioncontrol/guidelines/disinfection/disinfection-methods/chemical.html
Wash well in tap water?
The preferred treatment for root extraction is to flush well with bleach!
It is also the preferred disinfectant for cpr manikins.
Alcohol evaporates really well. Big drops can be pushed by blowing (or compressed air if the idea of putting your mouth there doesn’t appeal to you) on the inlet side of the cannula. Whatever thin coating is left will quickly evaporate and then you can blow the vapours again with the same technique
I absolutely agree you can kill any “bugs”; the challenge is getting the stuff out of the inside of the cannula afterwards.
Let’s say you used IPA or some similar “alcohol”. Even the tiniest bit of it, left behind, is going to make the user really ill when they take the first breath. Any form of chlorine would be even better 
as I know only too well from exposure to the stuff, in the “much safer” tablet form which nevertheless needs disposable gloves and best to do any handling outdoors in free air.
I believe @kwlf may know more about disinfection issues.
